Exchange Coupling in Homo- and Heterodinuclear Complexes CuIIM

Aug 1, 1994 - Deliberate Synthesis for Magnetostructural Study of Linear Tetranuclear Complexes BMnMnB, ... Simon Petrie and Robert Stranger. Inorgani...
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3990

Znorg. Chem. 1994, 33, 3990-4001

Exchange Coupling in Homo- and Heterodinuclear Complexes CunM [M = Cr(III), Mn(III), Mn(II), Fe(III), Co(III), Co(II), Ni(II), Cu(II), Zn(II)]. Synthesis, Structures, and Spectroscopic Properties Frank Birkelbach,+ Manuela Winter,? Ulrich Fl&ke,* Hans-Jiirgen Haupt,; Christian Butzlaff,g Marek Lengen,l Eckhard Bill,# Alfred X. Trautwein,g Karl Wieghardt,? and Phalguni Chaudhuri'vt Anorganische Chemie I, Ruhr-Universitat, D-44780 Bochum, Germany, Allgemeine Anorganische und Analytische Chemie, Universitat-GesamthohschulePaderborn, D-33098 Paderborn, Germany, and Institut fur Physik, Medizinische Universitat, D-23538 Liibeck, Germany Received December 14, 1993"

A series of heterodinuclear complexes CuIIM, where M = Cr(II1) (l),Mn(II1) (2), Mn(I1) (3), Fe(II1) (4), Co(I1) (5), Co(I11) (6), Ni(I1) (7), Cu(I1) (8), and Zn(I1) (9),containing the oximato dianion (DopnZ-)as bridging ligand and 1,4,7-trimethyl-1,4,7-triazacyclononane (L) as one of the two capping ligands have been synthesized by using the [Cu(DopnH)]+ cation (HzDopn = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,lO-dione dioxime) as a ligand for the different MLn+ centers. The compounds have been characterized on the basis of IR, electronic, and EPR spectroscopy and variable-temperature (2-295 K) magnetic susceptibility measurements. The dinuclear complexes are quasi-isostructural with the copper(I1) ion in a distorted square pyramidal environment, CuN40, and the M ion, except for that in 8, is six-coordinate with the MN303 or MN302C1 coordination sphere. For M = Cu (8), the coordination geometry of M with the C U N ~ Ochromophore Z is also square pyramidal. The crystal and molecular structures of the compounds [(DO~~)CU~~(OHZ)C~~~~(OCH~)L](C~~~)Z.HZO (1) and [ (Dopn)Cu1I(pCH3C0O)MnIIIL](C104)2.2Hz0(2) have been established by X-ray diffraction. 1crystallizes in the monoclinic system space groupP2~/n,withcellconstantsa=13.096(3)A,b= 17.933(4)&c= 15.994(3)&@= 113.49(3)O,V = 3444.9(13) A3, and 2 = 4. The structure consists of oximato-bridged CuI1Cr1I1dications and noncoordinated perchlorate anions, with a Cw C r distance of 3.86 A. The crystal data for 2 are as follows: orthorhombic, space group P212121,a = 12.275(4)& b = 14.171(9)A,c= 19.780(3)& V=3441(2)A3,Z=4. Thestructureconsistsofasix-coordinate Mn(II1) center, MnN303, and the copper(I1) center has an N40 donor set. An acetate group bridges the manganese and copper ions with a Cu. .Mn separation of 3.54 A. A low-quality X-ray structure determination for the CuIIFeIII complex is also reported. Analysis of the susceptibility data yields a strong antiferromagnetic interaction (2J = -596 cm-') between adjacent Cu(I1) ions in 8, showing once again that bridging oximes are good mediators for exchange interactions. The strength of the effectiveantiferromagnetic interaction decreases with increasing number of unpaired electrons in this series, 8 > 7 > 5 > 4 3. Moderately strong ferromagnetic interactions have been observed for Cu1IMn1l1(2) (25 = +lo9 cm-l) and CuI1Cr1I*(1) (2J = +37 cm-I). A qualitative rationale has been provided for the difference in magnetic behaviors. The X-band EPR spectra (3-77 K) have been measured to establish the ground states of the dinuclear complexes. Well-resolved S = 2 EPR spectra for different heterometal systems have been observed.

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Introduction The study of the exchange interaction14 between paramagnetic metal centers through multiatom bridges has been one of the most active research fields in coordination chemistry with the aim of understanding fundamental factors governingthe magnetic properties of transition metal compounds and finding appropriate systemsapplicable as building units for the design of new materials. Additionally, the importance of exchange coupling in multimetal proteinsShas stimulated much interest in exploring the ability of bridging multiatom ligands to mediate exchange coupling in M(bridging 1igand)M' systems. Both homo- and heteropolyRuhr-Universitilt Bochum. Universitilt-GesamthochschulePaderborn. 6 Medizinische Universitet zu Liibeck. e Abstract Dublished in Advance ACS Abstracts, Julv 15. 1994. Hatfield,'W. E. In Theory and Applications of kolehdar Paramagnefism; Boudreaux, E. S., Mulay, L. N., Eds.; Wiley: New York, 1976;p t

350.

Bencini,A.; Gatteschi, D. EPR of Exchange CoupledSysfems;SpringerVerlag: Berlin, 1990. Kahn, 0.Molecular Magnefism;VCH Verlagsgesellschaft: Weinheim, Germany, 1993. Magnefic Molecular Materials; Gatteschi, D., Kahn, O., Miller, J. S., Palacio, F., Eds.; NATO AS1 Series E, Vol. 198; Kluwer Academic: Dordrecht, The Netherlands, 1990. Solomon, E. I. In Mefal Cluster in Profeins;Que, L., Jr., Ed.; American Chemical Society: Washington, DC, 1988; p 116.

0020- 166919411333-3990$04.50/0

metallic systems provide opportunity to study experimentallyand theoretically fundamental electronic processes such as electron exchangein biological metallic sites and/or their chemical models. Metal ions assembled in such a multimetal system can exhibit magnetic properties drastically different from those of the individual ions due to electron exchange phenomena. New exchange pathways can be expected for heteropolynuclear complexes, where unusual sets of magnetic orbitals can be brought into close proximity; hence investigations of a series of heteropolynuclear complexes might be more informative in comparison to those of homopolynuclear complexes. The heteropolymetallic systems are of interest to both biologistsand bioinorganic chemists investigating the structure and function of the polynuclear metal centers in proteins and to physicists or physical inorganic chemists searching for new magnetic materials. With the aim of providing some answers to questions regarding the effectiveness of polyatomic bridging ligands like oximes and their metal complexes in propagating exchange interactions, we recently described6a series of dimethylglyoximato-bridgedlinear heterotrinuclear complexes of general formula

where MA= Fe(III), Mn(III), or Mn(IV), MB= Zn(II), Cu(II), 0 1994 American Chemical Society

Inorganic Chemistry, Vol. 33, No. 18, 1994 3991

Exchange Coupling in Cu"M Complexes Ni(II), Co(II), Fe(II), or Mn(II), and L represents the simple tridentate cyclic amine 1,4,7-trimethyl- 1,4,7-triazacyclononane, which coordinates facially in octahedral complexes. In continuation of our earlier interest in heterobimetallic systems,' we have prepared a series of compounds with the following structural motifs:

12+ '* Or

H3C

CH,

or H3C

CH3

y3

1

2+

Or

'+

(M = Cr(III), Mn(III), Mn(II), Fe(III), Co(III), Co(II), Ni(II), Cu(II), Zn(I1) and X = C1-, CHBO-) This has been accomplished by using [Cu(DopnH)(OH2)](ClO.#JO as a ligand for a metal center. HzDopn stands for 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,lO-dione dioxime

H,Dopn = C

N

N-OH

1 C - l

/

H3C

\

CU3

We report here the syntheses and magnetic and spectroscopic properties of the aforementioned compounds, together with crystal structures of the CuWrlI1and CuIIMnIIIcompounds. Throughout this paper, the compounds are denoted by the metal centers only; the macrocyclic amine and the oxime ligands are omitted for simplicity.

Experimental Section The macrocycle 1,4,7-trimethyl-1,4,7-triazacyclononane(=L) was prepared as described previously.* 3,9-Dimethyl-4,8-diazaundeca-3,8diene-2,lO-dione dioxime (HzDopn) and its mononuclear copper(I1) complex were obtained by the literature m e t h o d ~ . ~All J ~other starting materials were commercially available and were of reagent grade. Elemental analyses (C, H, N) were performed by the Microanalytical Laboratory, Ruhr-UniversitHt Bochum. Copper and nickel were determined gravimetrically by using N-benzoyl-N-phenylhydroxylamineand (a) Chaudhuri, P.; Winter, M.; Fleischhauer, P.; Haase, W.; FIBrke, U.; Haupt,H.-J. J.Chem.Soc.,Chem.Commun. 1990,1728. (b)Chaudhuri, P.;Winter, M.; Della Vedova, B. P. C.; Fleischhauer, P.; Haase, W.; FlBrke, U.; Haupt, H.-J. Inorg. Chem. 1991,30,4777. (c) Chaudhuri, P.; Winter, M.; Birkelbach, F.; Fleischhauer, P.;Haase, W.; FlBrke, U.; Haupt, H.-J. Inorg. Chem. 1991, 30, 4291. See for example: Chaudhuri,P.;Winter, M.; Kiippers, H.-J.; Wieghardt, K.; Nuber, B.; Weiss, J. Inorg. Chem. 1987, 26, 3302. Wieghardt, K.; Chaudhuri, P.;Nuber, B.; Weiss, J. Inorg. Chem. 1982, 21, 3086. Uhlig, E.;Friedrich, M. Z. Anorg. Allg. Chem. 1966, 343, 299. GagnC, R . J. Am. Chem. SOC.1976, 88,6709.

dimethylglyoxime, respectively. Zinc was determined by atomic absorption spectrometry. Quantitative determination of other metals was performed spectrophotometrically: chromium as chromate; iron, manganese, and cobalt as their dipicolinic acid complexes. The perchlorate anion was determined gravimetrically as tetraphenylarsonium perchlorate. Electronic absorption spectra were measured on a Perkin-Elmer Lambda 9 spectrophotometer in a methanolic solution. Fourier transform infrared spectroscopy on KBr pellets was performed on a Perkin-Elmer 1720X FT-IR instrument. Magnetic susceptibilities of powdered samples were recorded on a SQUID magnetometer (MPMS, Quantum Design) in the temperature range 2-295 K with an applied field of 1 T. Experimental susceptibility data were corrected for the underlying diamagnetism using Pascal's constants. The X-band EPR spectra of the polycrystalline material either as solid or in solution were recorded at various temperatures between 3 and 77 K with a Bruker ER 200 D-SRC spectrometer equipped with a standard TE 102 cavity, an Oxford Instruments liquid helium continuous-flow cryostat, an NMR gaussmeter, a frequency meter, and a data acquisition system (own development). Syntheses of the Compounds. The synthons [Cu(DopnH)(OHz)]C104-H20,9 LCrBr3,' and LFeC13ll were prepared by the literature procedures. [(Dopn)Cun(OH2)Crm(OCH3)L](C104)~H~0 (1). To a suspension of 0.46 g (1 mmol) of LCrBr3 in 30 mL of methanol was slowly added 0.62 g of AgC104.H20 (2.8 mmol) with stirring. The suspension was refluxed under argon for 0.5 h; during this time a blue-violet solution with a concomitant formation of AgBr resulted. Precipitated AgBr was filtered off, and the clear blue-violet solution was charged with a solid sample (0.4 g, 1 mmol) of [Cu(DopnH)(OH2)]C104 and 1 mL of triethylamine. The resulting red-brown solution was refluxed for 0.5 h, and NaCIOeH20 (0.5 g) was added. Upon standing at ambient temperature, the mixture deposited red-brown crystals. These were filtered off and air-dried. One of these crystals was used in the structural characterization of the complex reported below. Yield: 0.51 g (-66%). Anal. Calcd for [ C ~ ~ H ~ N ~ O ~ C U C C, ~ J31.88; ( C ~ H, O ~5.86; ) ~ :N, 12.39; Cu, 8.03; Cr, 6.57; C104, 25.14. Found: C, 31.3; H, 5.7; N, 12.6; Cu, 8.3; Cr, 6.6; c104, 25.3. [(Dopn)Cun(p-ooC~3)MmL](C104)~2H*0 (2). A solution of the cyclic amine (0.17 g, 1 mmol) in 40 mL of methanol was treated with a sample of manganese(II1) acetate (0.26 g, 1 mmol) under vigorous stirring in a round-bottomed flask. After 0.25 h of stirring, the resulting red-brown solution was charged with a sample of [Cu(DopnH)(OHz)]c104 (0.44 g, 1 mmol) and with sodium methoxide (0.14 g, 2.5 mmol). Thevery darksolution wasstirred for a further 2 hat ambient temperature, followed by an addition of NaClOcH20 (0.14 g). The dark solution was filtered to remove any solid particles. The solution kept at room temperature provided deep brown (almost black) crystals. The crystals were collected by filtration and air-dried. Yield: 0.46 (-56%). Anal. Calcd for [ C ~ ~ H ~ S N ~ ~ ~ C U MC, ~32.14; ] ( CH, IO 5.64; ~ )N,~ 11.93; : Cu, 7.73; Mn, 6.68; c104, 24.20. Found: C, 32.5; H, 5.4; N, 12.0; Cu, 7.1; Mn, 6.7; c104, 24.5. [(D~~~)C@(~-~~CCH~)MIPL](PF~)~~H~O (24. Complex21 was obtained similarly to complex 2 with sodium hexafluorophosphate instead of sodium perchlorate used as the anion source. Dark brown crystals were obtained. Yield: 0.40 g (-44%). Anal. Calcd for [ C ~ ~ H ~ N ~ O ~ C U MC, ~ 28.94; ] ( P FH, ~ )5.08; ~ : N, 10.74; Cu, 6.96; Mn, 6.02. Found: C, 29.0; H, 5.20; N, 10.8; Cu, 7.3; Mn, 6.4. [(Dopn)Cun(p-ooCCHj)MnnLI(CH)4)(3). All operations were done strictly under an argon atmosphere. Complex 3 was obtained as black needles in a manner similar to that for 2 using manganese(I1) acetate, Mn(OAc)r4H20, instead of "Mn111(OAc)3" as the manganese source. The compound in the solid state is air-stable. Yield: 0.30 g (-42%). Anal. Calcd for [ C ~ ~ H ~ Z N ~ O ~ M ~ C UC,] 38.49; ( C I OH, ~ )6.17; : N, 14.28; Cu, 9.26; Mn, 8.00; c104, 14.49. Found: C, 38.6; H, 6.4; N, 14.0; Cu, 8.9; Mn, 8.1; clod, 14.7. [(Dopn)Cun(OH~)F@(C)L](C04)~(4). A suspension of LFeCI3 (0.33 g, 1 mmol) and [Cu(DopnH)(OH2)]C104 (0.44 g, 1 mmol) in water (40 mL) containing triethylamine (1 mL) was stirred at room temperature for 1 h. To the resulting clear dark brown solution was added NaC104.H20 (0.5 g). After the mixture had stood at ambient temperature for 2 days, dark brown needle-shaped crystals separated from the solution. These were filtered off and air-dried. Yield: 0.62 g ( 1 1) Chaudhuri,

P.;Winter, M.; Wieghardt, K.; Gehring, S.;Haase, W.; Nuber, B.; Weiss, J. Inorg. Chem. 1988, 27, 1564.

3992 Inorganic Chemistry, Vol. 33,. No. 18, 1994

Birkelbach et al.

(-80%). Anal. Calcd for [C~~H~~N~O~CICUF~](CIO~)~: C, 30.75; H, Table 1. Crystallographic Data for [(DO~~)C~~~(OH~)C~~~~(OCHI)L] (C104)2.H20 (1) and 5.29;N, 12.56;Cu,8.13;Fe,7.15;C104,25.46. Found: C,30.9;H,5.4; [(Dopn)C U ~ ~ ( ~ C H ~ MnlIIL] C O O )(Clod 2'2H20 (2) N, 12.6; Cu, 7.9; Fe, 6.8; clod, 25.5. [(Dopn)Cun(r-ooCCII,)F~L](CIO~)~.H~O (Sa). To an aqueous solution of sodium acetate (1 g in 40 mL of H20) containingtriethylamine chem formula C 791.10 Z I H ~ ~ N ~ O I ~ C I ~ C822.05 CT~CZUH M N ~ O I ~ C I ~ C U M ~ (1 mL) were added LFeC13 (0.33 g, 1 mmol) and [Cu(DopnH)(OH2)]fw (CIO,) (0.44g, 1 mmol). The suspensionwasstirredat room temperature crystal system monoclinic orthorhombic for 1 h, yielding a clear dark brown solution. Sodium perchlorate hydrate space group P21/n 1" (0.5 g) was added, the solution was filtered to remove any solid particles, 13.096(3) 12.275(4) a, A and the filtrate was kept at ambient temperature for 2 days. Dark brown 17.933(4) 14.171(9) b, A crystals separated from the solution. These were filtered off and air15.994(3) 19.780(3) c, A 113.49(3) dried. Yield 0.5 g (62%). Anal. Calcd for [CZ~HCIN~O~F~CU](CIO~)~: %t deg v,A3 3444.9(13) 3441(2) C, 32.83; H, 5.51; N, 12.18; Fe, 6.94; Cu, 7.89; ClO4, 24.71. Found: Z 4 4 C, 32.7; H, 5.6; N, 12.3; Fe, 7.1; Cu, 8.0; clod, 24.6. 1.525 1.587 DCalcdl g cm-) [(Dopn)Cun(OH~)C~(Cl)L](C104) (5). All operations were perX(Mo Ka),A 0.710 73 0.710 73 formed strictly under an argon atmosphere. To a rapidly stirred and p, mm-1 1.155 1.213 degassed solution of 1,4,7-trimethyl-1,4,7-triazacyclononane (0.085 g, 0.5 R4 10.35 3.76 mmol) in 20 mL of water was added a sample of CoClr6H20 (0.12 g, 9.65 4.20 0.5 mmol), upon which a light blue precipitate of presumably cobaltous 293 293 hydroxide appeared. A sample of [Cu(DopnH)(OH2)] (Clod (0.22 g, IPcII)/ZPoL Rw = [Zw/(lFol- IFc1)2/ZdFd']'/2. 0.5 mmol) and 0.5 mL of triethylamine were added to the suspension under constant stirring and mild warming. Stirring was continued for absorption correction12 was carried out. The scattering factors13 for 0.5 h until a nearly clear solution was obtained. The solution was filtered neutral non-hydrogen atoms were corrected for both the real and the under argon to remove any solid particles. To the clear solution was imaginary components of anomalous dispersion. The structures were added a degassed solutionof NaCIO4.H20 (0.8 g) in water (5 mL). After determined by Patterson and Fourier methods for 1 and direct methods 1 h, the precipitated black-brown needles were collected and argon-dried. for 2 (SHELXTL PLUS). The structures were refined by a full-matrix The dried compound in the solid state is air-stable. Yield: 0.15 g (44%). least-squares technique; the function minimized was Zw(lFd - pc[)2 Anal. Calcd for [C~OH~~N~O~CUCO(CI)](CIO~): C, 35.07; H, 6.03; N, where l / w = a2(F)+ 0.003P for the CuIICrIII (1) and l/w = a2(F) + 14.31;C10~,14.52;Cu,9.28;Co,8.60. Found: C,35.5;H,6.0;N,14.4; 0.0008Pfor the Cu1IMn1l1(2)compound. Idealizedpositions of H atoms C104, 14.6; CU, 9.2; CO. 8.5. bound to carbon atoms were calculated (C-H = 0.96 A) and included Compound Sa, [(DO~~)CU~~(~-OOCCH~)C~~~L] (c104), was obtained in the refinement cycle. similarly to complex 5 with Co(OAc)2+4H20as the cobalt(I1) source. A large number of dark red needles of the Cu1ICr1I1complex, 1, had [(Dopn)Cun(OH~)C@L(Cl)](ClO4)~ (6). Complex 6 was obtained to be examined before a rather suitable specimen of the size 0.24 X 0.24 as dark red-brown crystals in a manner similar to that for 5 in the presence X 0.14 mm3could be selected,thoughit still sufferedfrompoor diffraction of air. Yield: 0.18 g (46%). Anal. Calcd for [ C ~ O H ~ ~ N ~ O ~ C U C O C quality I]and power. Cr, Cu, CI, and 0 atoms were refined anisotropically (C104)2: C, 29.88; H, 5.27; N, 12.50; ClO4, 25.36; CU,8.09; CO,7.51. for 1. Perchlorate oxygen atoms of 1 showed large displacement Found: C, 30.1; H, 5.0; N, 12.5; clod, 25.4; Cu, 8.3; Co, 7.6. parameters, indicating partial disorder of the perchlorate ions, which [(Dopn)Cun(OH~)NinL(OHz)](C104)~H~0 (7). To a solution of Nicould not be resolved. Refinement converged at R , = 9.65%. (C104)2.6H20 (0.18 g, 0.5 mmol) in 20 mL of water was added 0.5 mmol The diffraction intensities of an approximately 0.58 X 0.20 X 0.25 (0.085 g) of the cyclic amine, yielding a light blue precipitate of Nimm3 black prism crystal of 2 were collected. All non-hydrogen atoms (0H)z. The suspension was charged with a sample of [Cu(DopnH)for the CulIMnlI1compound,2, were refined anisotropically. The carbon (OH2)]C104(0.22 g, 0.5 mmol) and 0.5 mL of triethylamine. The mixed atom C(20), being statistically disordered over two sites, was refined solution was refluxed for 20 min and hot-filtered. The cooled solution with site occupancy factor 0.5 (split model). Refinement converged at yielded within a few hours brown needles, which were filtered off and Rw = 4.20%. Final positional parameters are presented in Tables 2 and air-dried. Yield: 0.23 g (58%). Anal. Calcd for [ C ~ O H ~ ~ N ~ O ~ C U N I - selected interatomic distances and angles are given in Tables 4 3,~while (C104)2: C, 30.61; H, 5.78; N, 12.49; clod, 25.35; Cu, 8.10; Ni, 7.48. and 5 for the CulICrlI1 and CulIMnlI1compounds, respectively. Found: C, 30.5; H, 5.7; N, 12.5; C104, 25.3; Cu, 8.2; Ni, 7.8. Results and Discussion Compound 713,[(DO~~)CUI~(~-OOCCH~)N~~~L] (c104), was obtained in a manner similar to that for 7 by using Ni(OAc)~4H20as the nickel Synthesis. The monomeric [Cu(DopnH)(OH2)]C104dissolves source, together with 1 g of sodium acetate. inmethanolorwaterin thepresenceofa basewith theconcomitant [(hpn)Cun(OH~)CunL](C104)~2H~0 (8). A 0.22 g (0.5 mmol) formation of a neutral species [Cu(Dopn)(OH,)]O, at least in sample of [Cu(DopnH)(OH2)](ClO4) was dissolved on warming in 20 part, as is evident from the formation of the dinuclear complexes mL of water by an addition of 0.1 g of NaOH. A second solution containing the Cu(Dopn) unit. T h e function of added base is to containing Cu(C104)y6HzO (0.19 g, 0.5 mmol) and the cyclic amine provide a medium needed for thedeprotonationof the0.s .He.-0 (0.085 g, 0.5 mmol) in 5 mL of water was added to the first solution. groups present in the solid[Cu(DopnH)(OHz)]+, with the copper Within a short time, brown needles precipitated and were separated by ions present in square pyramidal environments. The presumably filtration and air-dried. Yield: 0.29 g (75%). Anal. Calcd for square pyramidal neutral species [Cu(Dopn)(OH2)]0 produced [ C ~ O H ~ ~ N , ~ ~ C U ~ C, ](C 30.42; I O ~H, ) ~5.74; : N, 12.42; clod, 25.19; Cu, 16.09. Found: C, 30.0; H, 5.7; N, 12.3; c104, 25.3; Cu, 15.8. in this way can now function as a ligand for the coordinatively unsaturated ML3+Or 2+ units. In the presence of a counterion, [(Dopn)Cun(OH~)ZnnL(OH~)](CIO~)~H~O (9). Complex 9 was prepared as dark red crystals in a manner similar to that for 8 by using e.g. C104-, dark crystals a r e assembled in this manner in good Zn(C104)26H20 instead of Cu(C104)2 as the zinc source. Yield: 0.28 yields (6040%). T h e same type of reaction in the presence of g (71%). Anal. Calcd for [C~~H~~N.IO~CUZ~](CIO~)~: C, 30.35; H, acetate ions affords complexes containing a p2-bridging acetate 5.73;N,12.39;C104,25.13;Cu,8.03;Zn,8.26.Found: C,30.4;H,5.7; ion. N, 12.4; ClO4, 25.5; Cu, 8.2; Zn, 8.4. infrared Spectra. T h e presence or absence of certain bands in Caution! Although we experienced no difficultieswith thecompounds the generally complicated IR spectra has been utilized to establish isolated as their perchloratesalts, theunpredictable behavior of perchlorate the nature of t h e complexes. Relevant bands a r e listed in Table salts necessitates extreme caution in their handling. 6. All of t h e perchlorate salts show strong bands near 1090Crystal Structure Determinations. Diffraction data were obtained on a Siemens P4 diffractometer, using graphite-monochromatized Mo K a (12) SHELXTL-PLUS program package (PC version) by G. M.Sheldrick, radiation at 293 K. Pertinentcrystallographicparameters are summarized Universitiit G6ttingen. in Table 1. The data were corrected for Lorentz and polarization effects, (1 3) International Tablesfor X-ray Crystallography;Kynwh: Birmingham, but it was not necessary to account for crystal decay. An empirical England, 1974; Vol. 4.

Inorganic Chemistry, Vol. 33, No. 18, 1994 3993

Exchange Coupling in Cu"M Complexes Table 2. Atomic Coordinates ( X l v ) and Equivalent Isotropic

Displacement Coefficients (AZX 10') for 1

Table 3. Atomic Coordinates (X lo4) and Equivalent Isotropic

Displacement Coefficients (A2 X 103) for 2

X

Y

z

U(W)'

X

Y

z

5567 5627(4) 11533(17) 10474(18) 3989( 19) 6057(25) 5158(23) 52 1O( 26) 5978(22) 6 163(28) 5606(24) 4957( 19) 5931(17) 3743( 17) 7 loo( 17) 4073(28) 5193(28) 5962(27) 5960(28) 3936(27) 3327(30) 3399(30) 7 16l(33) 5408(38) 5092(30) 4724(40) 5356(33) 5173(53) 6470(34) 6943(42) 6371(29) 6866(44) 5945(45) 6072(46) 6 162(49) 7615(41) 11612(54) 11053(80) 11018(77) 12437(47) 10773(98) 10916(34) 9390(34) 10809(29) 8781(31)

2928 2637(3) 357( 14) 6399(11) 3018(15) 3271(18) 1816(18) 2 104(21) 358 1(19) 3759(21) 2152(22) 2001(14) 3525(14) 3259( 13) 2266( 13) 3598(22) 3871(21) 2744(21) 1980(20) 1897(22) 2384(23) 3386(24) 3569(26) 1091(24) 1452(28) 735(27) 1514(30) 775(38) 4329(28) 5056(28) 4220(26) 4860(3 1) 2291(32) 3693(33) 2924(36) 22 14(29) -10(28) 932(44) 21(35) 43 l(44) 7060(33) 6003(27) 6426(41) 6142(22) 1634(22)

7100 9508(3) 8397(12) 11998(12) 9274( 15) 10755(20) 10283(19) 7654(22) 8112(18) 6617(24) 6229(21) 8422( 15) 8978(15) 6342(14) 9903( 14) 9997(23) 10468(24) 11463(22) 11222(22) 10058(24) 9291(25) 8369(23) 10992(26) 10049( 32) 727 l(26) 7502(32) 6405(28) 58 lO(35) 7078(30) 6956(30) 8026(25) 8726(33) 5458(36) 5608(36) 5411(41) 9324(33) 9077(34) 8229(50) 761 5(43) 8421(55) 11989(61) 11528(19) 11620(28) 12873(23) 7165(25)

68(3) 38(3) 98(10) 106(10) N7) 63(10) 57(10) 77(11) 50(9) 80( 12) 67(11) 62(8) 56(7) 46(7) 52(7) 63(12) 51(12) 49(10) 48(11) 56( 12) 67(12) 69(13) 93( 15) 104(17) 58(12) 121(18) 77(15) 217(32) 75(14) llO(18) 54( 12) 129(20) 137(21) 153(23) 161(26) 134(20) 259(48) 314(66) 303(59) 267(62) 361(120) 189(29) 312(44) 137(24) 164(15)

-285 2145(1) 3880(5) 285 l(6) 2819(5) 799(4) 729(5) -1 196(5) -1117(5) 1837(3) 1756(4) -961(4) 665(4) 4521 (7) 3765(7) 3239(8) 2761(8) 395 5 (6) 4240(7) 3919(8) 2052(8) 2141(7) 512(6) 1224(7) -625(6) -1 107(8) -744(7) -1 246(9) 391(7) 1064(9) -228 l(7) -229 l(8) -2477(18) -2737 ( 12) -325(7) -777(7) 5288(2) 5810(7) 5211(7) 4228(7) 5894(7) 396(2) -71 5 ( 5 ) 613(7) 1022(7) 646(8) 7135(8) 6200(7)

5506 4344( 1) 4797(4) 3011(4) 4065(4) 5955(4) 4781(4) 5413( 5 ) 6547(5) 5 6 15 (3) 4479(4) 4406(4) 3747(4) 3984(6) 3228(6) 2558(5) 3005(5) 4442( 8) 5120(6) 5603(6) 2365(5) 4477(7) 6665(5) 7115(5) 6954(5) 7672(6) 5008(5) 4892(7) 4641(5) 4 146(7) 6777(7) 583 l(8) 6741(19) 5992( 14) 3842(5) 3217(6) 7590(1) 8430(5) 7516(5) 7580(7) 6827(5) 10509(2) 10718(6) 9565(4) 11056(5) 10691(8) 4884(7) 3142(6)

9858 9373(1) 9592(3) 9605(3) 84 16(3) 9 177(3) 10448(3) 10668(3) 9427(4) 9 103(2) 10299(2) 9224(2) 9066(3) 9825(5) 10067(5) 8964(4) 8358(4) 8372(4) 8903(5) 10090(5 ) 9947(5) 7859(3) 8809(4) 8302(4) 8930(4) 8465(6) 11172(4) 11865(4) 11058(3) 11563(4) 9609(6) 10707(6) 10275(10) 10102(11) 8932(4) 8375(5) 8385(1) 8214(4) 9090(4) 8119(5) 8129(4) 8 130(1) 8249(4) 8225(4) 8575(5) 7461(4) 8503(5) 8311(5)

'Equivalent isotropic U defined as one-third of the trace of the orthogonalized Ut, tensor.

1100 cm-1 (antisymmetric stretch) and sharp bands a t 620-625 cm-1 (antisymmetric bend), indicative of uncoordinated perchlorate anions. Since the spectra of all complexes 1-9 are quite similar, the discussion is confined to the most important vibrations of the 4000400cm-1 region in relation to the structure. The monomeric [Cu(DopnH)(OH~)]C104.H~0 has appreciable IR absorption in the region of 2300 cm-1 due to the OH stretching vibrations of the hydrogen-bonded OH0 group. These absorptions are missing in the spectra of the dinuclear complexes, indicating that the enolic hydrogen atoms are lost on chelation. The medium-strong bands at 1 192-1 245 cm-1 are assignableI4 to the N O stretching vibration. The second N O infrared absorption could not be observed for every dinuclear complex because of the occasional superposition of the bands originating from the perchlorate anions. However, for the hexafluorophosphate salt of the cation in complex 2a, the second NO stretch was identified unambiguously at 1 1 16 cm-l. The v(CN) vibration is assigned to the band in the wavenumber regions 1633-1622 cm-1 for the imine and 1489-1558 cm-1 for (14) (a) Blinc, R.; Hadzi, D. J . Chem. SOC.A 1958,4536. (b) Burger, K.; Ruff, I.; Ruff, F. J . inorg. N u l . Chem. 1965, 27, 179. (c) Caton, J. E.; Banks, C. V. Inorg. Chem. 1967,6, 1670.

U(W)'

a Equivalent isotropic U defined as one-third of the trace of the orthogonalized Ui, tensor.

the oxime groups. The v(CN) vibration of the oximes for the dinuclear complexes containing trivalent metal ions is situated a t a frequency significantly higher than that for the complexes containing the corresponding divalent metal ions, where these vibrations are found a t 1490 cm-l for Mn(I1) and 1515 cm-1 for Co(I1). This is in accord with the concept that on binuclear complex formation the positively charged ML3+ unit stabilizes the negative charge on oxygen of the oximate function15 and thus increases the double-bond character of the CN bond, which is expressed as a rise in the frequency. The strong bands in the wavenumber regions 1578-1571 and 1428-1410 cm-1 for 2,2a, 3,4a, Sa, and 7a are indicative of bridging acetato groups (Av(CO)= 168-143 cm-I). Electronic Spectra. Substantial energetic and distributional changes in the ?r-electron cloud of the C=N group are observed on complex formation by the oxime ligand H1Dopn, as is evidenced from IR spectroscopy. These changes should also be, in principle, observable in the optical spectra for the dinuclear complexes. Hence the optical spectra of the dinuclear complexes, together (15) Chakravorty, A. Coord. Chem. Reu. 1974, 13, 1.

3994 Inorganic Chemistry, Vol. 33, No. 18, 1994

Birkelbach et al.

Table 4. Selected Bond Lengths (A) and Angles (deg) for [(Dopn)Cu(OH~)Cr(OCH3)L](C10~)2.H20 (1) (Esd's in

Parentheses) Cu-N(4) Cu-N(6) Cu-O(3) Cr-N(2) Cr-O(1) Cr-0(4) ~(4)--0(1) ~(5)-0(2) N(6)-C(14) N(7)-C(12) N(4)-Cu-N(5) N(5)-Cu-N(6) N(5)-Cu-N(7) N(4)-Cu-0(3) N(6)-Cu-O(3) N(1)-Cr-N(2) N(2)-Cr-N(3) 1) N(2)-Cr-O( N( 1)-Cr-0(2) N(3)-Cr-O(2) N( l)-Cr-0(4) N(3)-Cr-O(4) 0(2)-Cr-0(4)

1.876(39) 1.977(41) 2.285(19) 2.166(31) 1.968(23) 1.895(22) 1.406(49) 1.414(41) 1.230(60) 1.252(66) 97.1(15) 81.2(15) 162.9(11) 92.9(11) 95.1(11) 82.4(11) 81.9(12) 167.9(13) 91.6( 10)

166.7(13) 171.l(10) 93.1(11) 94.3(10)

Cu-N(5) Cu-N(7) Cr-N(1) Cr-N(3) Cr-0(2)

1.984(37) 2.173(26) 2.165(35) 1.920(27)

N(4)-C( 10) N(5)-C(16)

1.301(61) 1.286(56)

N(4)-Cu-N(6) N(4)-Cu-N(6) N(6)-Cu-N(7) N(5)-Cu-0(3) N(7)-Cu-O(3) N(l)-Cr-N(3) N(1)-Cr-O( 1) N(3)-Cr-O( 1) N(2)-Cr-O(2) 0(1)-Cr-O(2) N(2)-Cr-O(4) 0(1)-Cr-0(4)

1.893(30)

172.0(13) 81.9(16)

97.5(16) lOO.O(l0) 97.1(10)

79.8(11) 88.1(10) 89.1(11) 87.0( 12)

100.9(10) 91.2( 11) 97.3(10)

Table 5. Selected Bond Lengths (A) and Angles (deg) for [(Dopn)Cu(p-OOCCHp)MnL](ClO4)~2H~O (2) (Esd's in

Parentheses) Cu-N(4) Cu-N(6) Cu-O( 3)

Mn-N(2) Mn-O( 1) Mn-0(4) N(4)-0(1) N(5)-0(2)

N( 4)-Cu-N( 5 ) N (5)-Cu-N (6) N(5)-CU-N( 7) N(4)-Cu-0(3) N(6)-Cu-0(3) N( 1)-Mn-N(2) N(2)-Mn-N(3) N(2)-Mn-O( 1) N(1)-Mn-0(2) N(3)-Mn-O(2) N( 1)-Mn-O(4) N(3)-Mn-O(4) 0(2)-Mn-O(4)

1.996(6) 1.958(7) 2.166(5) 2.128(6) 1.916(5)

Cu-N(5) Cu-N(7) Mn-N(l) Mn-N(3) Mn-0(2)

1.992(6) 1.986(7) 2.266(6) 2.104(6) 1.902(5)

N(4)-C(10) N(5)-C(16) N(6)-C( 14) N(7)-C(12)

1.291(9) 1.291(9) 1.277(11) 1.290(11)

2.093(6) 1.371(7)

1.363(8)

98.2(2) 81.0(3)

162.9(3) 95.4(2) 101.9(2) 80.1(2)

82.2(2) 167.0(2) 9 1.4(2) 169.8(2) 170.1(2) 90.2(2) 95.9(2)

N (4)-Cu--N (6) N(4)-Cu-N(7) N(6)-Cu--N(7) N(5)-Cu-O(3) N(7)-Cu-O( 3) N(1)-Mn-N(3) N( 1)-Mn-O( 1) N(3)-Mn-O( 1) N(2)-Mn-O(2) O( 1)-Mn-O(2) N(2)-Mn-O(4) O( l)-Mn-O(4)

162.5(3) 79.0(2) 96.2(3) 102.0(2) 95.1(2) 8 1.7(2) 88.4(2) 90.1 (2)

89.1(2) 97.2(2) 93.3(2) 97.3(2)

with the nionomeric [Cu(DopnH)(OH2)]C104, the free oxime H2Dopn, and its deprotonated form Dopn2- in basic medium, have been measured in methanol in the range 200-1 200 nm. The absorption maxima with the corresponding extinction coefficients aregiven in Table 7. The spectra of thecomplexes are dominated by charge-transfer transitions in the UV-vis regions. The absorption maximum of the free ligand HzDopn a t 227 nm is due to r-r* transitions of the C=N group and shifts, as is expected, to lower energy at 276 nm in basic medium due to deprotonation of the OH groups. For the mononuclear [Cu(DopnH)(OH2)]+, apart from the ligand band a t 237 nm, there are absorptions a t 274 and 300 nm. Metal to ligand chargetransfer (MLCT) transitions can occur in complexes where the unsaturated ligands like oximes, whichcontain empty antibonding ?r orbitals, are bonded to oxidizable metals. Judged on the basis of high extinction coefficients, the last mentioned two bands are ascribed to these charge-transfer transitions. The transition is thought to be the (yz f izx)--s*,,i,, in character. Mediumstrong bands are found a t 486 nm for Cu(DopnH)+ and 535 nm

for Cu(Dopn)O(Cu(DopnH)+in basic medium) on thelow-energy side of the charge-transfer bands. This transition is considered to be a spin-allowed d-d transition, as has been described previously in the literature.16 In the wavelength range 200-365 nm, the spectra of the dinuclear complexes disclose character nearly identical with that of the Cu(Dopn)O unit, indicating that the energy states of *-electron system of the Dopn2- anion suffer no substantial alterations on complex formation. However, the extinction coefficients measured at nearly identical wavelengths show significant differences. The dinuclear complexes in general exhibit three bands in the region 200-365 nm due to the intraligand r-u* and MLCT transitions withvery highextinction coefficients. These complexes are dark brown to practically black and owe their origin of color to these CT transitions. The symmetryforbidden d-d bands are in many cases obscured by the more intense bands due to symmetry-allowed CT transitions. Interestingly, we have not observed any d-d band for 1 that could be unambiguously assigned to the Cr(II1) center. Complex 2 exhibits a very broad intense band a t 560-575 nm. Probably this band, d-d in nature, originates from both the Cu(I1) and the 5T2, 5E,transitions at the Mn(II1) center. The sharp band a t 412 nm for 3 can be assigned to the Mn(I1) center due to the 4Al,(G), 4Eg(G) 6A1, tran~itions,'~ although this predicted forbidden transition should be weak in intensitiy. This formally forbidden band for the Mn(I1) chromophore is activated by an exchange mechanism, as might be the shoulder at -490 nm for 4. Complex 5 exhibits several d-d bands in the range 425-1010 nm due to the transitions at Cu(I1) and Co(I1) centers. However, the weak band at 1010 nm can be unambiguously assigned to the 4T2g 4Tl, transition of the Co(I1) center. The Cu(I1) bands for 7 are difficult to recognize. On the other hand, the bands at 787 and 1015 nm definitely originate from the Ni(1I) center due to 3T1,(F) 3A2, and 3T2, 3A2, transitions. The band at 928 nm of complex 8 originates from the Cu(CgH21N3) unit. This assignment is in complete accord with our earlier observations in Cu(I1) chemistry with this macrocyclic amine.18 The Cu1IZn1Icomplex, 9,exhibits a single d-d band a t 520 nm due to the presence of d9 Cu(I1). On the basis of this and our earlier observations in Cu(I1) chemistry with the oxime ligands,19 we assign the shoulders and peaks in the range 500-590 nm to the spin-allowed d-d transitions occurring mostly a t the Cu(Dopn) unit, strongly indicating the presence of five-coordinate copper(I1) ions. The extinction coefficients are in some cases large, in spite of the Laporte g ++ g selection rule, because of the extensive mixing of the metal d orbitals with the ligand orbitals and because of their proximity to other C T bands. It has been shown by HathawayZ0that it is possible to predict the stereochemistry of the local copper(I1) environment in Cu(11) complexes of unknown crystal structure from the positions and intensities of d-d transitions of CuX5 chromophores. In general, trigonal bipyramidal complexes with 2Al ground states exhibit a single relatively intense band at 12 500 f 1500 cm-l; on the other hand, the electronicspectra of square based pyramidal complexes consist of two clearly resolved bands covering the range (1500 A 2000) cm-I. On the basis of the above knowledge, a pseudo square pyramidal geometry is assigned to Cu(I1) centers in all complexes synthesized (Table 7) rather than a trigonal bipyramidal geometry. The electronic spectral results indicate

-

-

-

-

-

(16) Nishida, Y.;Hayashida, K.;Sumita, A.; Kida, S . Inorg. Chim.Acta 1978, 31, 19. (17) Lever, A. B. P. InorgunicElectronicSpectroscopy; Elsevier: Amsterdam, 1984. (18) Chaudhuri, P.;Oder, K. J . Chem. Soc., Dalton Tram. 1990, 1597. (19) Chaudhuri, P.; Winter, M.; Della VUova, B. P. C.; Bill, E.;Trautwcin, A. X.;Gehring, S.;Fleischhauer, P.; Nuber,B.; Weiss, J. Inorg. Chem. 1991, 30, 2148. (20) (a) Hathaway, B. J.; Tomlinson,A. A. G. Coord.Chem.Rev.1970,5, 1. (b) Hathaway, B. J.; Billing, D. E. Coord. Chem. Rev.1970,5, 143. (c) Hathaway, B. J. Strucr. Bonding (Berlin)1984, 57,55.

Inorganic Chemistry, Vol. 33, No. 18, 1994 3995

Exchange Coupling in CuIIM Complexes Table 6. Selected IR Spectral Datau comulex

Y, cm-1

[(DO~~)CU~~(OH~)C~~~~(OCH~)L](C~O~).H~O (1) [( D o ~ ~ ) C U ~ ~ ( ~ - O O C (C104)2*2H20 C H ~ ) M ~ (2) ~~~L]

[(Dopn)CulI(p-OOCCH3)MnlIIL](PFs) r2H20 ( 2 4

[(Do~~)CU~~(~-OOCCH~)M~~~L] (Clod) (3) [(Dopn)CulI(OH2) Fell1(Cl)L] (c104)2 (4) [( D o ~ ~ ) C U ~ ~ ( ~ - O O C(C104)rH20 C H ~ ) F ~ (413) ~~~L]

[(Dopn)CuII(OHz)Co"( C1)L] (c104) (5)

[(DO~~)CU~~(~-OOCCH~)C~~~L] (Sa) [(Dopn)CulI(OH2)Co111(CI)L] (C104)~(6)

[(Do~~)CU~~(OH~)N~~~(OH~)L] (C104)2*H20( 7 ) [(DO~~)CU~~(~-OOCCH~)N~~IL] (c104) (74 [(DO~~)CU~~(OH~)CU~~L](C~O~)~~H~O (8)

[(Do~~)CU~~(OH~)Z~~~(OH~)L] ( C 1 0 4 ) ~ H ~(9) o

u(0H) 3518 m (sh) v(CN) 1633 m (sh), 1536 m (sh) v(N0) 1219 m (sh), 1145 s (sh) v(0H) 3640,3430 s (sh) v(CN) 1632 m (sh), 1588 s (sh) v(N0) 1233 m (sh) v(C00) 1572 s (sh), 1419 s (sh) v(0H) 3647 m (sh), 3436 s (br) v(CN) 1633 m (sh) v(N0) 1192m(sh),1116w(sh) v(C00) 1571 s (sh), 1428 m (sh) v(CN) 1612 m (sh), 1490 s (sh) v(N0) 1234 s (sh), 1147 s (sh) v(C00) 1572 s (sh), 1413 s (sh) v(0H) 3620 m (sh), 3515 m (sh) v(CN) 1633 m (sh), 1538 m (sh) v(N0) 1216 m (sh), 1150 s (sh) v(0H) 3640,3436 m (sh) v(CN) 1631 m (sh) v(N0) 1150 (sh) v(C00) 1571, 1410s (sh) v(0H) 3582,3502 m (sh) v(CN) 1613 m (sh), 1515 s (sh) u(N0) 1233, 1150 s (sh) v(CN) 1618 (sh), 1495 m (sh) v(N0) 1236, 1147 s (sh) v(C00) 1578, 1411 s (sh) v(0H) 3637 m (sh), 3430 m (br) v(CN) 1613 m (sh), 1538 s (sh) v(N0) 1220 m (sh) v(0H) 3490 s(br) v(CN) 1620 m (sh), 1500 s (sh) v(N0) 1240 m (sh), 1156 s (sh) v(CN) 1618 m (sh), 1489 s (sh) v(N0) 1245, 1152 vs (sh) v(C00) 1577 vs (sh), 1411 s (sh) v(0H) 3576,3540 m (sh) v(CN) 1625 m (sh), 1521 s (sh) v(N0) 1226 m (sh), 1147 s (sh) v(0H) 3590 s (sh), 3436 s (br) v(CN) 1622 m (sh), 1510 s (sh) v(N0) 1237 s (sh), 1151 vs (sh)

Key: vs = very strong; s = strong; m = medium; w = weak; sh = sharp; br = broad.

Table 7. Electronic Spectral Data for the Dinuclear Complexes in Methanol at Ambient Temperature Am=. nm (e, L mol-'cm-1) comulex Cu1*CrIII(OCH3)(1) CuI1MnII1(OAc) (2) Cu1IMn1I(OAc) (3) CullFelll(C1)(4) C U ~ ~ C O ~( 6~) ~ ( C ~ ) Cu"Co"(C1) (5) CuIINi~I(0H~) (7) Cu1ICuI1(8) CuIIZnII(OH2) (9) [Cu(dopnH)]+ [Cu(dopn)lo dopnHz dopn2-

220 sh (17 500), 236 (18 740), 278 (13 040), -530sh (350) 245 (18 320), 280 sh (14 loo), 311 (13 820), 560-575 br (1020) 253 (14 710), 275 sh (12 400), 320 (10 450), 412 (923), 450 sh (600), 540 (603), 585 sh (570) 245 (20 640), -270 sh (15 500), 345 sh (7340), 490 sh (380), 565 sh (220). 1250 (4) 240 (23 950), 299 (18 180), 365 sh (5300), 505-520 sh (506) 250 (15 270), 308 (12 220), 425 sh (lOOO), 540 sh (440), 585 sh (360), 673 (199), 1010 (9.8) 250 (15 470), 275 sh (11 700), 319 (11 210), 787 (31), 1015 (19) 249 (16 990), 300 sh (11 300), 325 (13 490), 435 (2470), 575 sh (630), 928 (24) 247 (16 780), 275 sh (11 000), 314 (12 540), 520 (233) 237 (13 880), 274 (7720), 300 sh (6400), 486 (205) 251 (12 520), 282 (12 420), 310 sh (9400), 535 (400) 227 (17 100) 276 (>13 000)

that the complexes 1-9 are stable and retain their discrete 1.876-1.977 A and are considered as normal covalent bonds. The dinuclear entity also in solution. axial Cu-0(3) bond is longer, 2.285(19) A, as is expected for Molecular Structure of [(J~~~)CU~~(OH~)C~~(OCH~)L]square pyramidal complexes of copper(11) and has been observed (C104)rHzO (1). The complex molecule consists of a dicationic earlier.19 The copper ion is 0.21 A out of the best basal plane dinuclear unit, two disordered perchlorate anions, and a water comprising the four nitrogen atoms N(4)N(5)N(6)N(7) in the molecule. The cation together with the atom-labeling scheme is directionofthecoordinatedwateroxygenO(3). Thus themetrical used in Figure 1. Selected bond lengths and angles are listed in parameters for the Cu center in 1 are similar in magnitude to Table 4. The copper ion is in a distorted square pyramidal those reported in the literature for the [Cu(DopnH)(OHz)]+ environment with four nitrogens in the basal plane and the fifth, complex cation.21 apical, position occupied by a water molecule. Each fivemembered ring containing cu an Oxime nitrogen (21) (a) Bertrand,J. A,; Smith,J. H.; van D.G.Inorg. Chem.1977, and an imine nitrogen; the six-membered chelate ring includes 6, 1484. (b) Anderson, 0. P.; Packard, A. B. Inorg. Chem. 1979, 7 , two imine nitrogens. The Cu-N bond lengths fall in the range 1940.

3996 Inorganic Chemistry, Vol. 33, No. 18, 1994

Birkelbach et al.

c5

c3

c20

c4

Figure 1. Molecular structure of the dinuclear CulICrlI1cation in 1, showing the atom-numbering scheme.

Figure 3. Intermolecular hydrogen-bonding network in 2. Figure 2. ORTEP view of the dinuclear

CuIIMnlII cation

in 2.

structural data concerning the ligand parts of the complex are in good agreement with the previous studies dealing with compoundsof the same ligands and do not warrant any additional The chromium coordination geometry is distorted octahedral comment. The ring conformation of the macrocyclicamine ligand with three nitrogen atoms from the facially coordinatedtridentate macrocyclic amine and three oxygen atoms, O( 1) and O(2) from L in the complex 2 is 666. The structure of the complex molecule the bridging oximate group and the third from a monodentate consists of a dicationic asymmetric unit, two well-separated methoxy group, O(4). The Cr-N (average 2.16(2) A) and perchlorate anions, and two molecules of water of crystallization. The X-ray structure confirms that a heterodinuclear complex Cr-0 (average 1.92(2) A) distancescorrespond to the literature values for Cr(II1) complexes with this macrocyclic amine.' A with a Cw .Mn distance of 3.539 A has indeed been formed as deviation from idealized orthogonal geometry is found for the a result of the sharing, in a very broad sense, of a face between ligand L, the N-Cr-N angles ranging between 79.8(11) and a square pyramid and an octahedron. The coordination environment around the copper atom is distorted square pyramidal with 82.4(1 l)', whereas 0-Cr-0 angles fall between 94.3(10) and 100.9(10)'. The chromium ion is displaced by 0.15 A from the four nitrogens at the equatorialplanes and the carboxylateoxygen mean basal N(2)N(3)0( 1)0(2) atoms toward the apical oxygen O(3) of the bridging acetate group at the axial position, Cu-0atom O(4) of the methoxy group. (3) = 2.166(5) A. The Cu-N bond lengths fall in the range 1.958(7)-1.992(6) A, slightly elongated compared with theCu-N The binuclear skeleton is not coplanar but is slightly bent with a Cw .Cr separation of 3.86 A. The dihedral angle between the bonds21 in [Cu(DopnH)]C104 (1.937(5)-1.961(5) A). The planes CuN(4)N(5)N(6)N(7) andCrN(2)N(3)0( 1)0(2) is 14'. copper ion is displaced by 0.3 8, from the mean basal plane of It is interesting to note that the coordinated water, 0(3), at the the four nitrogenatoms, N(4)N(5)N(6)N(7),of theDopnligand Cucenteris situated at an antiposition with respect to themethoxy toward the apical oxygen atom O(3). group, 0(4), of the Cr(II1) center. Thus the structure can be One of the oxygen atoms of a perchlorate anion is situated at described as resulting from the sharing of an edge between a an axial position, trans to 0(3), of the Cu ion with a separation square pyramid and an octahedron. of Cue -0(6) = 3.544 A and can be considered as nonbonding. The ligand L exhibits no unexpected features. Comparatively An intermolecular hydrogen-bonding network (Figure 3) is present between the oxygen atoms O(7) and O(8)of a perchlorate anion short C-C bond lengths (average 1.44(2) A) between the methylene groups of the macrocyclic amine ligand L may be Cl(l), two molecules of water, O(1w) and 0(2w), and the O(3) attributed to the effects of libration. atom of the acetate group with the following bond separations: Molecular Structure of [(Dopn)C~~~(a-CHjCoo)Mn~~L]0 ( 7 ) - 0 ( 2 ~ ) = 2.985,0(2~)-0( Iw) = 2.748,0( l ~ ) - 0 ( 3 ) = 2.820,0( lw)--O(8) = 3.233 A. Hydrogen atomsof the water (ClO&-ZH20 (2). Figure 2 shows a perspectiveviewof thecation molecules could not be located, except one, H(2w), which was in 2 with the atom-labeling scheme in the asymmetric unit. Selected bond distances and angles are listed in Table 5. The introduced in the refinement cycle.

.

a

-

Exchange Coupling in Cu"M Complexes

Inorganic Chemistry, Vol. 33, No. 18, 1994 3997

C26

c39

Figure 4. Structure of the dinuclear dication CullFelll in 4.

The manganese coordination geometry is distorted octahedral with three nitrogen atoms from the facially coordinated tridentate macrocyclicamine and three oxygen atoms, two from the bridging oximate group and one from the bridging acetate group. The manganese ion is out of the plane comprising 0(1)0(2)N(2)N(3) by0.15 A toward the oxygen atom O(4) of the acetate group. The largest deviation from idealized 90' interbond angles is 9.9', which occurs within the five-membered C-C-N-Mn-N chelate rings, the N-Mn-N angles ranging between 80.1 (2) and 82.3(2)', whereas the 0-Mn-0 angles fall between 95.9(2) and 97.3(2)'. 0(1), 0(2), N(2), and N(3) from the basal plane of the tetragonally distorted octahedron for the manganese ion with Mn-O(av) = 1.909(7) Aand Mn-N(av) = 2.1 16(12) A. The axial Mn-0(4) and Mn-N(l) bond lengths, 2.093(6) and 2.266(6) A, respectively, are substantially elongated as a consequence of the Jahn-Teller distortion of the Mn(II1) ion. Thus the bond lengths are consistent with a d4 high-spin electron configuration of the Mn(II1) center. The binuclear cation is not coplanar but is bent with a dihedral angle between theplanesCuN(4)N(5)N(6)N(7)and MnO( 1)O(2)N(2)N(3) of 40.6'. Structure of [(Dopn)Cu~~(0H~)FeU~(Cl)L](Cl0~)2 (4LZ2Although the analytical and spectroscopic data unambiguously showed the presence of a dinuclear CuFe core as the smallest unit in the cation, an X-ray analysis was undertaken to remove the doubts regarding connectivity. Unfortunately, crystals of the cation as its perchlorate salt diffract X-rays very weakly. In spite of the high R factor and large standard deviations due to the limited data of a weakly diffracting small crystal, the crystal structure analysis of 4 confirmed its heterobinuclear structure. Because of its unacceptable quality, we are refraining from publishing the crystal data in detail. The structure consists of distinct [(DO~~)C~~I(OH~)F~~I~(C~)L]~+ cations and noncoordinatively bound perchlorate anions (Figure 4). The asymmetric unit cell contains two independent molecules. The iron center Fe(2) is 6-fold coordinated, the N(10), N(8) of the cyclic amine and 0(4), O(5) of the oxime oxygens forming the equatorial plane of an octahedron, the apexes of which are occupied by a nitrogen N(9) of the ligand L and a chlorine atom Cl(2). The metrical parameters and coordination geometry of the Cu center are similar to those of the Cu center in 1. The Fe-N (average 2.21 A) and Fe-0 (average 1.94 A) bond lengths are in accord with a d5 high-spin electron configuration of the Fe(II1) center. In contrast to the structure of 1, the coordinated water molecule O(6) at the Cu center and the chloride ion Cl(2) a t the Fe center

d

(22) [ C ~ H , I N ~ O ~ C I C U C10&, F ~ ] monoclinic space group, Pc, u = 8.317f ) A, b = 24.341(9) , c = 15.877(6) A, @ = 90.30(2)", V = 3214.2 3, Z = 4, final R = 0.109 for 2884 unique observed intensities.

g-factors 20 6 4 3

2.0 1.5

1.0

A

dX" dB

I: I

0

1

200

/ -

, 400

600

800

B b-r]

Figure 5. EPR spectra of methanolic solutions of complexes 1, 3, and 4 at 4.2 K. Experimental conditions: modulation amplitude 1 mT, modulation frequency 100 kHz, microwave power 20 pW, microwave frequency 9.433 GHz.

are in the cis positions. As is expected, the cation is bent with a dihedral angle of 23.2' between the CuN4and FeN202planes. The nonbonded Cw .Fe separation is 3.66 A. The iron ion is situated 0.29 A above the basal plane toward the apical chlorine atom. EPR Studies. X-band EPR spectra of complexes 1-9 were recorded both on powder samples and in methanolic solutions a t low temperature (3.0-77 K) in order to establish the electronic ground state of the heterodinuclear complexes. Significant contributions from excited states were not observed in the measured temperature range, due to strong exchange splitting of spin states. This is consistent with magnetic susceptibility measurements, described below. Solid Sa, C U ~ ~ C O with ~ I ,an apparently diamagnetic ground state is EPR silent under our experimental conditions. Interestingly, three other integer-spin systems (S = 2) of the series, Cu"CrIII (l),CuIIMntt(3), and CulIFetI1 (4), are EPR active, which reveals weak zero-field splitting within the S = 2 multiplets of these compounds. EPR spectra of methanol solutions of 1, 3, and 4 are depicted in Figure 5. Polycrystalline samples also yield integer-spin EPR spectra; however, due to intermolecular spin coupling in the solid state, they hardly resemble the solution spectra

-

3998 Inorganic Chemistry, Vol. 33, No. 18, 1994

Birkelbach et al.

g-factors 20. 10. 6.0

4.0

3.0

I .' '' " ' " ' " ' ' " ' ~ ~ ' 0

100

" "

2.0

'

"

1 .

" "

300

200

1.5

'

"

"

" " " "

400

'I

500

B [mTI

Figure 6. EPR spectrum of polycrystalline complex 2 at 77 K. Experimental conditions: modulation amplitude 1 mT, modulation frequency 100 kHz,microwave power 200 pW, microwave frequency 9.430 GHz.

and, hence, werediscarded. The resonancesof the solution spectra are broad and extend over a wide field range from zero to more than 500 mT. (Weak narrow lines at g 2 are due to S = contaminations in the solution and will not be regarded.) The wide distribution of integer-spin signals indicates that, under experimental conditions of X-band EPR, zero-field interaction and Zeeman interaction are comparable and correspond to the energy of X-band resonances (hu = 0.3 cm-l). Under these conditions magnetic substates are severely mixed and level splittings depend strongly on field strength and field direction within the molecular frame. The EPR resonances, therefore, depend on the orientation of molecules in frozen solution and, hence, are spread over a wide range of applied fields. From such complex integer-spin EPR spectra, g tensors of the spin quintets cannot be derived without explicit simulations. The situation would be more transparent under the followingconditions. EPRactive S = 2 systems with clearly dominating zero-field interaction (D > hv) would show the typical ug = 12" pattern, as observed for cytochrome c oxidase and related Fe-Cu model complexes.23 Those signals arise from pseudo-"Am = 4" transitions within distinct and energetically isolated "ms = f2" sublevels. On the other hand, vanishing zero-field interaction (D